Hypoxia followed by reoxygenation is commonly used as a model to investigate pathology associated with ischemia/reperfusion as the latter condition is present in several disease states including stroke. In animal models, hypoxia followed by reoxygenation has been shown to cause tight junction protein abnormalities, increased BBB paracellular permeability and edema however, a complete mechanism leading to these pathologies is still undefined. von Willebrand Factor (VWF) is a glycoprotein that is only synthesized by endothelial cells and megakaryocytes. While it is known that VWF is expressed abundantly by cerebral endothelial cells (CECs), very little is known about the role of VWF in endothelial biology, particularly, in regulation of the BBB under stressful conditions. Data we have generated demonstrate that VWF-deficient mice have significantly less BBB permeability than wild type in a model of generalized hypoxia/reoxygenation. VWF is a major ligand for platelets during endothelial activation and preliminary data we have gathered support a role for platelets in survival of exposure to hypoxia. Platelets are best known for their role in hemostasis and inflammation and the primary ligand for platelet binding to the endothelium and exposed subendothelium is VWF. Platelets can activate endothelium but are also activated by inflamed endothelium. Data supporting alteration of platelet number and function after exposure to hypoxia have been documented. However, studies have yielded conflicting results leaving much room for advancements in this field. Intriguingly, a role for platelets as potentiators of increased paracellular permeability in human brain endothelial cell cultures has been documented and recent literature suggests a role for platelets in various CNS diseases involving the BBB. The role of VWF and platelets in BBB biology is understudied and warrants further investigation, thus our overall objective is to determine the extent VWF and platelets promote BBB permeability under stressful conditions. To accomplish this, we will use a model of generalized normobaric hypoxia followed by reoxygenation. In our first aim, we propose to examine the role of plasma vs. subendothelial VWF in increased BBB permeability associated with generalized hypoxia/reoxygenation. Secondly, we will determine the extent that platelet interactions with VWF and the endothelium lead to increased BBB permeability. We propose to accomplish these aims using knock out mouse technology, BBB permeability assays, confocal microscopy, platelet-depletion studies and tight junction protein assays. The studies outlined in this proposal aim to further our understanding of how a glycoprotein expressed by brain microvasculature interacts with a cell type of hematopoietic lineage to influence the BBB during hypoxia and thus are directly relevant to the mission of NINDS, specifically the neural environment division.